The present invention relates to a method of an apparatus for controlling the ignition timing of an internal combustion engine.
A well-known ignition timing control system of an internal combustion engine controls the ignition timing by detecting the flow rate of the intake air or the pneumatic pressure in the intake manifold and the rotational speed as engine parameters indicative of operation conditions. An optimum ignition timing is calculated from the detected engine parameters using a function which represents a relationship of optimum ignition timing relative to the engine parameters. The ignition timing is adjusted responsive to the calculated value. In general, systems of this type are provided with a service input terminal (IS terminal) for initially adjusting the ignition timing in the factory or for servicing the ignition timing. If a predetermined electrical signal is applied to the IS terminal, e.g., a ground-potential signal (signal having positive logic of "0"), by grounding the IS terminal using a specially designed detachable connector, the ignition timing control system controls the ignition timing to a fixed ignition timing irrespective of the operating condition of the engine. Therefore, it becomes possible to adjust or to service the reference position of the crank angle and to adjust the ignition timing.
However, if the detachable connector is inadvertently not removed after the adjustment has been finished, and if the operation of the engine is continued with the predetermined signal being applied to the IS terminal, the ignition remains at the fixed timing, which gives rise to the occurrence of overheating of the engine, misfire, and damage to the ignition system by heat.